Just watching the first few minutes, the AmiDock author has some work to do (hint hint Stefan Robl). Ironically, AmiDock already has a "stack"-like concept in it's subdocks. However, it's not as convenient as OSX Leopard's. You can emulate the grid stack layout by dragging and dropping a directory onto the dock; clicking on it will then bring up that directory in a window. Once again, similar, but not quite as nice.
Coverflow is definitely nice and we definitely don't have anything like it. Workbench is overdue for an overhaul.
Quicklook like functionality could be implemented via the datatypes system and multiview, if more datatypes were made. I've always suggested that things like Flash and PDF viewers should be turned into datatypes.
Time machine looks like a really well done backup system. The fact that all other OS features can be used directly on backups is impressive. I'm guessing that the backups are mounted like a filesystem.
We have the start to spaces with screens and switcher3D (OS4 only). It definitely needs a lot more work though.
iChat theatre like functionality could once again be done via more datatypes, if we had an iChat program to begin with.
It's clear that Apple have worked hard on making organization of information easy. Most of it is taking existing stuff, and just adding extra functionality that's easier to use. The result is definitely impressive.
Hans
